One conventional method of forming an insulated roof is to build-up a roof consisting of a concrete channel slab roof deck. Up to six layers, including insulation, membrane and stone ballast layers, are built-up on top of a concrete channel slab roof deck to form the insulated roof system. This type of roof system is complicated, difficult to install and to maintain, and has a large dead load (approximately 27 pounds per square foot) due to the combination of up to 7 layers. Each channel slab typically covers only a single structural purlin span. If one of the channel slab supports were to fail, the channel slab would fall inside the building. Further, concrete channel slabs are susceptible to corrosion, which can cause concrete in the roof deck to break apart and fall inside the building.
Other known methods of forming an insulated roof include joining together fiberglass sandwich panels. Conventional fiberglass sandwich panels employ the structure of a foam core sandwiched between outer fiberglass skins. One conventional method of forming such a panel is by blowing the foam into an air cavity between the fiberglass skins, then curing the panel. This process of foam-cavity blowing and curing may cause inadequate layer attachment and subsequent delamination problems. Another conventional method of forming roof panels is by pultrusion. Panels formed by this method are limited to the width of the pultrusion machine (typically two feet, but a maximum of four feet). In addition, pultrusion cannot completely encapsulate the foam core, leaving exposed the front and rear ends of the foam core.
The shape of the fiberglass sandwich panel determines how a plurality of the panels will fit together to form a roof. It is known in the art to make two rectangular panels and to put them together in overlapping and offset relation. Panels having this shape generally have highly stressed corners and have a tendency to come apart at the point where two halves are connected. Another conventional panel shape is a panel having a tongue on one end and a groove on the other end. The panels fit together by inserting the tongue of one panel into the groove of another. This shape is especially suited for siding and steep sloped roof applications rather than flat roof applications. When applied to flat roofs, leaks have formed where the panels are joined.
Fiberglass roof panels have been fabricated using a variety of other methods. As representative of such art, reference may be had to U.S. Pat. No. 3,841,958 to Delorme. The Delorme patent discloses forming a fiberglass sandwich roof panel on a continuous bed by sealing a foam layer to top and bottom face sheets made of glass cloth using sprayed layers of thermosetting or epoxy resin. Also disclosed are the forming of lengthwise ribs of resin bonded to the glass and foam layers by spraying resin into recesses in the surface of the foam core, and the forming of depthwise ribs through the foam core layer to connect the top and bottom skin layers.
U.S. Pat. Nos. 3,874,980 and 4,073,997 to Richards disclose roof panels having a top layer of randomly dispersed chopped strand filaments in 15%-25% resin in a lightweight mat, and a bottom layer of glass fibrous board of heavier density and thickness. Alternating layers of asphalt and glass fibrous mat are applied over the upper layer of an installation.
Roof panels formed by foaming a foam layer between facing sheets of metal foil to expand and impregnate a glass mat consisting of multiple layers of parallel glass fibers are disclosed in U.S. Pat. Nos. 4,028,158, 4,284,683 and 4,346,133 all to Hipchen. U.S. Pat. No. 4,438,166 to Gluck discloses the addition of flame retardant coatings to a panel made by the method disclosed in the Hipchen patents.
U.S. Pat. No. 4,279,958 to Ahmad discloses another fiberglass sandwich roof panel in which alternate layers of glass fibrous mat and woven or nonwoven webs of organic fibers (such as nylon, cellulose, or rayon) are applied at the upper layer. Another fiberglass roof panel is disclosed in U.S. Pat. No. 4,774,794 to Grieb. This roof panel is formed by hand lay-up to attach a fiberglass mat to the surfaces of a foam core (in standard four-foot widths) then applying a coating mixture of cement, fiberglass roving, and acrylic adhesive. The panels may be interconnected with tongue-and-groove joints sealed with adhesive, spline joints sealed with adhesive, and/or keyed joints sealed with a backer rod and cement.
Finally, U.S. Pat. Nos. 4,288,951 and 4,320,605 to Carlson are directed to insulated roof panels comprising polystyrene which are formed into multi-span widths having rabbeted ends. The panels are joined in ship-lapped relation to form panel joints at the panel ends, which are filled with a backer rod and sealant. The joined insulation panels are then covered with lapped layers of fiberglass topsheet.
Although many attempts have been made in the prior art to provide a roofing system comprising a plurality of fiberglass sandwich panels, none suggest the use of a sandwich panel having two substantially parallel surfaces and a peripheral edge having a step shape or a roofing system comprising sandwich panels having two shapes with relative dimensions joined at ship-lap joints. For example, the Grieb patent only mentions standard four foot width panels joined at tongue and groove joints. The patents to Carlson only disclose panels having rabbeted ends. Further, none of the above-described patents teach a process for forming fiberglass sandwich panels having multi-span widths by hand lay-up in a mold of layers comprising a gel coat layer, a fiberglass skin layer and a foam core.
The present invention is directed to a lightweight roofing system that provides a safe, long lasting, leak-free and maintenance-free surface for any application that requires both structural strength and insulation, in particular, flat roof applications. More particularly, it is concerned with an insulated fiberglass sandwich panel and a method for its manufacture. Another aspect of the invention is the provision of a system of overlapping sandwich panels, wherein the panels have preselected strength specifications for selected end uses. Other aspects of the invention reside in forming panels in widths that cover several purlin spans (i.e. multi-span widths) and the easy installation of the panels to form a continuous roof assembly having joints formed by lapping the panel ends with a backer rod and sealant. The sandwich panel of the invention installed in this manner will provide an insulated roof system that overcomes delamination problems of prior roof panels, has reduced dead load (approximately 3 pounds per square foot), easier installation and maintenance, and more reliable service use (i.e. no leaks).
Accordingly, it is a broad object of the invention to provide an improved insulated roofing system for flat roof applications.
A more specific object of the invention is to provide a roofing system that provides a safe, long lasting, leak-free and maintenance-free insulated surface.
Another object of the invention is to provide a fiberglass sandwich panel for use in the insulated roofing system that is easy to install and will not delaminate.